#main{
    width: 408px;
    height:408px;
    background:white;
    border:2px solid gray;
    margin:0 auto;
    overflow: hidden;
}

h2{
    text-align: center;
}

#con{
    width:100%;
    height: 400px;
    position: relative;
    top: -400px;
    border-collapse: collapse;
}

.row{
    height: 100px;
    width: 100%;
}

.cell{
    height: 100px;
    width: 100px;
    float: left;
    border:rgb(54,74,129) 1px solid;
}
.black{
    background: black;
}

.btn{
    width: 100%;
    text-align: center;
}

.start{
    margin-top: 20px auto;
    width: 150px;
    height:50px;
    border-radius: 10px;
    background: yellowgreen;
    line-height: 50px;
    color: #fff;
}